The goal of this project was to evaluate by direct measurements the actual size of infarction following coronary artery occlusion in the rat and to measure the actual degree of alteration in infarct size following an intervention. To accomplish this goal infarct size was measured either 48 hours or 21 days after occlusion since the necrotic process is at its peak after 48 hours and scar formation is completed after 21 days. The size of myocardial infarctions was measured directly either by planimetry of serial histologic slices of the heart or by creatine kinase activity (CK) determination of the whole left ventricle. Using these techniques it was determined that hyaluronidase, cobra venom factor, reserpine, glucocorticoids and ibuprofen reduce significantly infarct size and result ultimately in more salvaged myocardium. Glucocorticoids in large doses, however, impair healing resulting in thin scars. Electronmicroscopic studies, in which the mechanisms of action of these interventions was examined indicate that propranolol protects preferentially the mitochondria, hyaluronidase conserves glycogen and glucocorticoids result in mummification of myocytes. In conclusion, several interventions were shown to reduce infarct size permanently resulting in more extensive areas of normal myocardium.